The primary purpose of target localization is to identify within a three-dimensional space the region in which deep brain stimulation (DBS) will produce optimal benefit. Further, targets must be identified and avoided, lest stimulation produce adverse effects. The primary targets for efficacy in the globus pallidus interna (GPi) and the ventral intermediate nucleus of the thalamus (Vim) are the appropriate homuncular representation within sensorimotor regions. With respect to the subthalamic nucleus (STN), it is just the sensorimotor region. Primary targets to be avoided include the posterior limb of the internal capsule in both the GPi, STN, and Vim; the optic tract in GPi; and the medial lemniscus and oculomotor nerve roots in STN DBS. To date, microelectrode recordings (MERs) of extracellular action potentials are the only effective mechanism. However, MERs add significantly to cost and risk.
It can be possible to use local field potentials; however, the issue is whether the resolution of local field potentials within the sensorimotor homunculus is sufficient to allow precise localization within a specific region of the homunculus as is necessary for larger structures such as GPi and Vim as well as to identify structures whose stimulation is to be avoided. Current interest of using local field potentials (LFPs) to identify regions of high beta oscillations are problematic and in the end, not of sufficient reliability.
Somatosensory evoked potentials from stimulation of the median nerve have been measured (Dinner D S, Neme S, Nair D, Montgomery E B Jr, Baker K B, Rezai A, Lüders H O. EEG and evoked potential recording from the subthalamic nucleus for deep brain stimulation of intractable epilepsy. Clin Neurophysiol. 2002 September; 113(9):1391-402). As shown in that work, evoked potentials in the subthalamic nucleus are relatively later than the appearance of the evoked potential recorded over the scalp and representing a cortex, consequently, recordings from the medial lemniscus precede those in the subthalamic nucleus. That work also shows phase reversal centered at the middle contact on the DBS lead which is evidence of origin of the evoked potential from within the subthalamic nucleus.
The objective of the person using the invention is to rapidly and efficiently physiologically identify specific regions in the nervous system, including but not limited to the brain, in order to accurately place therapeutic devices or agents, including but not limited to the deep brain stimulation (DBS) lead or injection cannula for biologics. Recording of long latency transcortical reflexes allows rapid assessment of the spinal cord such as but not limited to spinal cord surgery.